In recent years, a motor incorporating a driving circuit is often used in blowers for air conditioning. In the motor, a high-voltage power converter circuit and a stator are connected to each other. The motor is molded with thermosetting resin, such as unsaturated polyester resin. The direct-current power supply for motor driving is set to a voltage as high as maximum 325 volts (e.g., Patent Literature 1). Air conditioners are often used in areas where power supply situations are bad. The maximum of the voltage of the direct-current power supply tends to further increase.
A package for sealing an integrated circuit (hereinafter abbreviated as IC) has been reduced in size and a package for surface mounting is also often used. In particular, for an IC mounted on a power converter in a motor, the package for surface mounting is used in more cases because of a demand for size reduction (e.g., Patent Literature 2). However, ICs used in a blower motor for air conditioning or the like require relatively large allowable power consumption. Therefore, mounting needs to be contrived to efficiently radiate heat generated by the allowable power consumption.
An inverter circuit of a motor is provided with a resistor that is connected to the high potential (the positive electrode of the direct-current power supply) side of the circuit and is fused when an abnormal current occurs in the circuit, a shunt resistor for detecting an electric current flowing to the low potential (the negative electrode of the direct-current power supply) side of the circuit, and the like. However, in the inverter circuit configured in this way, an abnormal current flows to the shunt resistor as well. Therefore, when the shunt resistor is burnt out (disconnected) by the abnormal current, it is likely that the shunt resistor, which should originally have low resistance, has high resistance. Then, although a cause of the abnormal current is not eliminated in the inverter circuit, a flow of the electric current from the high potential side to the low potential side of the inverter circuit is hindered by the shunt resistor. Therefore, an electric current for fusing the resistor does not flow to the resistor connected to the high potential side of the inverter circuit and thus a state in which the resistor is not fused continues. That is, when the shunt resistor is burnt out by the abnormal current that occurs in the inverter circuit, because the resistor is not fused, the voltage corresponding to the abnormal current is continuously applied to the inverter circuit. Therefore, it is likely that the components of the inverter circuit, the motor, and the like are damaged.
As a method for solving such a problem, a power converter disclosed in Patent Literature 3 is configured to include a resistor connected to the high potential side of an inverter circuit and fused when a predetermined or larger abnormal current occurs, a shunt resistor connected to the low potential side of the inverter circuit, and a bypass circuit connected in parallel with the shunt resistor and causing the abnormal current to bypass the shunt resistor when the abnormal current flows. When the abnormal current occurs in the inverter circuit, because the abnormal current flows to the bypass circuit, burnout of the shunt resistor is prevented. Therefore, the shunt resistor is suppressed from being burnt out to have high resistance. Thus, even if an inexpensive resistor is used, it is possible to fuse the resistor. As a result, it is possible to interrupt the inverter circuit from a power supply side. Accordingly, it is possible to prevent an abnormal voltage from being applied to the components of the inverter circuit, the motor, and the like.